The present invention relates to the field of navigation of various objects, moving in inertial space and equipped with on-board inertial navigation systems.
Among such objects may be land-based and sea-going vehicles (motor vehicles, watercraft), as well as aircraft and spacecraft (airplanes, rockets, space vehicles).
A method is known for determining the position of a three-axis navigation system by simultaneously measuring gravitational acceleration and angular velocity of Earth rotation [1].
The method is mainly used for the initial alignment of inertial systems of objects which are stationary relative to Earth, wherewith the geographical coordinate system is often used as the basic coordinate system. The method cannot be applied to moving objects subjected to acceleration and angular velocity.
A method is known for determining the position of a three-axis navigation system in relation to a basic coordinate system set by known optical directions [2].
The method is used both for the initial alignment of the axis of a navigation system of stationary objects in accordance with known directions, for example, in the direction of selected stars, and in the process of movement of the object.
A method is also known for astronavigation in accordance with patent RU No. 2033949, IPC6 B64G {fraction (1/24)},  which provides for coincidence of a common plane of sensitivity of Earth and Polaris sensors, including a space vehicle""s longitudinal axis, with the plane xe2x80x9cearth""s centerxe2x80x94spacecraftxe2x80x94Polarisxe2x80x9d (based on measured yaw, pitch and roll angular errors), wherewith the inertial longitude of the spacecraft position is determined according to the azimuth of the rotation angle in the field of view of the star sensor of a selected star around the xe2x80x9cspacecraftxe2x80x94Polarisxe2x80x9d direction in relation to a reference base and taking into account the inertial longitude of that reference base, the parameters of which are stored. The reference basexe2x80x94a plane comprising xe2x80x9cspacecraftxe2x80x94Polarisxe2x80x9d and xe2x80x9cspacecraftxe2x80x94navigation starxe2x80x9d directionsxe2x80x94is characterized by an inertial longitude equal to the direct ascension of Polaris and is turned relative to the common plane of sensitivity of Earth and Polaris sensors by an angle equal to the angle between the plane containing the xe2x80x9cearth centerxe2x80x94Polarisxe2x80x9d and xe2x80x9cearth centerxe2x80x94celestial polexe2x80x9d direction and the plane containing the xe2x80x9cearth centerxe2x80x94Polarisxe2x80x9d and xe2x80x9cearth centerxe2x80x94navigation starxe2x80x9d direction.
These methods, however, require the presence of optical means on board the object, such as star sights, and optical contact with reference points. As regards land-based objects and atmospheric aerocraft prone to weathering, the method""s utilization is restricted by the employment of optical means.
The analog most similar to the proposed method for determining the position of reference axes in an inertial navigation system of an object in respect with the basic coordinates is the method based on the simultaneous measurement of the acceleration vector in the basic system and in the system being defined [3]. Wherewith the acceleration vector is measured in at least two trajectory points, where the measured acceleration vectors are unparallel.
This method may be employed only in those cases where the basic coordinate system and the object""s coordinate system experience the same acceleration, that is, the basic system""s carrier and the object are mechanically coupled and move along the same trajectory. For examplexe2x80x94an aircraft (object) on the deck of an aircraft carrier (carrier of the basic system), a rocket (object) aboard a carrier aircraft (carrier of the basic system).
The method is feasible in practice in those cases when the basic coordinate system is known with a better measurement accuracy than the coordinate system of the object, and also when the accuracy of the basic coordinate system is sufficient to solve the navigation task of the object.
In practice, these conditions are often not met and the method cannot be employed. For example, a launch vehicle should have an accuracy or orientation of the axes of the inertial system which is not worse than units of angular minutes, while a carrier aircraft at the moment of launch of a launch vehicle may have an orientation of the axes of the basic coordinate system with an error of tens of angular minutes.
The object of the present invention is to enhance the accuracy and reliability of determining the position of the reference axes in an inertial navigation system of a moving object, as well as to ensure all-weather determination.
This object is achieved in that in embodiment 1 of a method for determining the position of reference axes in an inertial navigation system of an object in respect with the basic coordinate system, comprising navigation measurements of an object moving in inertial space, in a basic coordinate system and in the inertial coordinate system of the object.
at moments of time ti and tixe2x88x921, the coordinates of the moving object are measured in a coordinate system of a global navigation system, like xe2x80x9cGLONASxe2x80x9d or/and xe2x80x9cNAVSTAR,xe2x80x9d selected as the basic coordinate system.
at the ti-tixe2x88x921 trajectory portion, the acceleration vector is measured in the inertial coordinate system of the object, in accordance with which the object""s coordinates are determined at the same moments of time ti and tixe2x88x921;
at the moments of time tj and tj+1 at an object trajectory portion which is not parallel with the portion of the preceding navigation measurements, similar measurements of the object""s coordinates are performed in the basic coordinate system and in the object""s inertial coordinate system;
then on the basis of the coordinates determined at each portion of the trajectory ti-ti+1 and tj-tjxe2x88x921, which are selected to be at least two, displacement vectors Li, Lj of the object are determined in the basic coordinate system LiB, LjB and in the object""s inertial coordinate system LiU, LjU;
next, the matrix of transfer between the basic coordinate system and the object""s inertial coordinate system is determined from the set of equations:
LiB=ALiU,
LjB=ALjU,
i,j=1 . . .n, ixe2x89xa0j,
where Axe2x80x94matrix of transfer from the basic coordinate system to the object""s inertial coordinate system,
nxe2x80x94number of trajectory portions;
then according to the matrix A components, the position of the reference axes in the inertial navigation system of the object is determined in relation to the basic system.
In embodiment 2 of a method for determining the position of reference axes in an inertial navigation system of an object with basic coordinates, comprising navigation measurements of an object moving in inertial space, in a basic coordinate system and in the inertial coordinate system of the object:
at moments of time ti and tixe2x88x921, the speed vector of the moving object is measured in a coordinate system of a global navigation system, like xe2x80x9cGLONASxe2x80x9d or/and xe2x80x9cNAVSTAR,xe2x80x9d selected as the basic coordinate system;
at the ti-ti+1 trajectory portion, the acceleration vector is measured in the inertial coordinate system of the object, in accordance with which the speed vector of the object is determined at the same moments of time ti and ti+1;
at the moments of time tj and tjxe2x88x921, at an object trajectory portion which is not parallel with the portion of the preceding navigation measurements, similar measurements of the object""s speed vector are performed in the basic coordinate system and in the object""s inertial coordinate system.
then on the basis of the speed vectors determined at each portion of the trajectory ti-ti+1 and tj-tj+1, which are selected to be at least two, the speed vector increments xcex94Vi and xcex94Vj of the object are determined in the basic coordinate system xcex94ViB, xcex94VjB and in the object""s inertial coordinate system xcex94ViU, xcex94VjU;
next, the matrix of transfer between the basic coordinate system and the object""s inertial coordinate system is determined from the set of equations:
xcex94ViB=Axcex94ViU,
xcex94VjB=Axcex94VjU,
i,j=1 . . .n, ixe2x89xa0j,
where Axe2x80x94matrix of transfer from the basic coordinate system to the object""s inertial coordinate system,
nxe2x80x94number of trajectory portions;
then according to the matrix A components, the position of the reference axes of the inertial navigation system of the object is determined in relation to the basic system.
In embodiment 3 of a method for determining the position of reference axes in an inertial navigation system of an object in respect with basic coordinates, comprising navigation measurements of an object moving in inertial space, in a basic coordinate system and in the inertial coordinate system of the object.
at moments of time ti and ti+1, the coordinates and speed vector of the moving object are measured in a coordinate system of a global navigation system, like xe2x80x9cGLONASxe2x80x9d or/and xe2x80x9cNAVSTAR,xe2x80x9d selected as the basic coordinate system;
at the ti-ti+1 trajectory phase, the acceleration vector is measured in the inertial coordinate system of the object, in accordance with which the object""s coordinates and speed vector are determined at the same moments of time ti and ti+1;
at the moments of time tj and tj+1, at an object trajectory portion which is not parallel with the portion of the preceding navigation measurements, similar measurements of the object""s coordinates and speed vector are performed in the basic coordinate system and in the object""s inertial coordinate system;
then on the basis of the coordinates and speed vectors determined at each portion of the trajectory ti-ti+1 and tj-tj+1, which are selected to be at least two, displacement vectors Li, Lj and speed vector increments xcex94Vi-xcex94Vj of the object are determined in the basic coordinate system LiB, LjB, xcex94ViB, xcex94VjB and in the object""s inertial coordinate system LiU, LjU, xcex94ViU, xcex94VjU;
next, the matrix of transfer between the basic coordinate system and the object""s inertial coordinate system is determined from the set of equations:
LiB=ALiU, xcex94ViB=Axcex94ViU
LjB=AliU, xcex94VjB=Axcex94VjU
i,j=1. . . n, ixe2x89xa0j,
where Axe2x80x94matrix of transition from the basic coordinate system to the object""s inertial coordinate system.
nxe2x80x94number of trajectory portions;
then according to the matrix A components, the position of the reference axes of the inertial navigation system of the object is determined in relation to the basic system.
According to the present method, a maneuver of an object moving along a rectilinear trajectory in inertial space is executed, which ensures at least two non-parallel trajectory portions where the mentioned navigation measurements are carried out.